1. Field of the Invention
This invention is concerned with plain bearings, in particular, oil lubricated bearings which require low friction, particularly static (break-away) friction.
Polytetrafluoroethylene (hereinafter referred to as "PTFE") has good tribological properties and is, therefore, often used as the lining material for a plain bearing. PTFE is, however, soft and weak and has an unacceptably high wear rate when used alone. Therefore, harder materials must be added to the PTFE lining to reduce wear and give an acceptable bearing life.
2. Description of the Related Art
Bearings are known which comprise a steel backing having a porous bronze sintered layer thereon and a lining layer infiltrated into pores of the sintered layer and standing proud of the sintered layer to provide a low-friction surface of the bearing. Such bearing layers comprise PTFE filled with either lead or molybdenum disulphide. However, these conventional materials tend to suffer from erosion effects when used under severe conditions in an oil-lubricated bearing. This is caused by cavitation brought about by the lubricating oil and results in the removal of the filled PTFE from the sinter by the action of the lubricating oil alone, without rubbing wear.
GB Patent Specification No 2,166,142B describes a bearing of this type in which an ionic fluoride, for example calcium fluoride, is included in the lining layer. This lining material shows enhanced cavitation erosion resistance while retaining desirable low friction properties. It is, however, desirable to provide a bearing of this type having even better erosion resistance properties.